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Conservation status
Scientific classification
Species:C. carpio
Subspecies:C. c. haematopterus
Trinomial name
Cyprinus carpio haematopterus[1]
(Linnaeus, 1758)
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This article is about the ornamental fish. For other uses, see Koi (disambiguation).
Conservation status
Scientific classification
Species:C. carpio
Subspecies:C. c. haematopterus
Trinomial name
Cyprinus carpio haematopterus[1]
(Linnaeus, 1758)
(video) Several Koi swim around in a pond in Japan.

Koi (?, English /ˈkɔɪ/, Japanese: [koꜜi]) or more specifically nishikigoi (錦鯉?, [niɕi̥kiꜜɡo.i], literally "brocaded carp"), are ornamental varieties of domesticated common carp (Cyprinus carpio) that are kept for decorative purposes in outdoor koi ponds or water gardens.

Koi varieties are distinguished by coloration, patterning, and scalation. Some of the major colors are white, black, red, yellow, blue, and cream. The most popular category of koi is the Gosanke, which is made up of the Kohaku, Taisho Sanshoku, and Showa Sanshoku varieties.


Carp are a large group of fish originally found in Central Europe and Asia. Various carp species were originally domesticated in East Asia, where they were used as food fish. Carp are coldwater fish, and their ability to survive and adapt to many climates and water conditions allowed the domesticated species to be propagated to many new locations, including Japan. Natural color mutations of these carp would have occurred across all populations. Carp were first bred for color mutations in China more than a thousand years ago, where selective breeding of the Prussian carp (Carassius gibelio) led to the development of the goldfish.[2]

The common carp was aquacultured as a food fish at least as far back as the fifth century BC in China, and in the Roman Empire during the spread of Christianity in Europe.[3] Common carp were bred for color in Japan in the 1820s, initially in the town of Ojiya in the Niigata prefecture on the northeastern coast of Honshu island. By the 20th century, a number of color patterns had been established, most notably the red-and-white Kohaku. The outside world was not aware of the development of color variations in koi until 1914, when the Niigata koi were exhibited at an annual exposition in Tokyo. From that time, interest in koi spread throughout Japan. It was from this original handful of Koi breeds that all other Nishikigoi types were bred, with the exception of the Ogon variety (single colored, metallic Koi) which was developed relatively recently.

The hobby of keeping koi eventually spread worldwide. Koi are now sold in many pet aquarium shops, with higher-quality fish available from specialist dealers.[4][5]

Extensive hybridization between different populations has muddled the historical zoogeography of the common carp. However, scientific consensus is that there are at least two subspecies of the common carp, one from Western Eurasia (Cyprinus carpio carpio) and another from East Asia (Cyprinus carpio haematopterus).[6] One recent study on the mitochondrial DNA of various common carp indicate that koi are of the East Asian subspecies.[6] However, another recent study on the mitochondrial DNA of koi have found that koi are descended from multiple lineages of common carp from both Western Eurasian and East Asian varieties.[7] This could be the result of koi being bred from a mix of East Asian and Western Eurasian carp varieties, or being bred exclusively from East Asian varieties and being subsequently hybridized with Western Eurasian varieties (the butterfly koi is one known product of such a cross). Which is true has not been resolved.


The word koi comes from Japanese, simply meaning "carp." It includes both the dull grey fish and the brightly colored varieties. What are known as koi in English are referred to more specifically as nishikigoi in Japan (literally meaning "brocaded carp"). In Japanese, koi is a homophone for another word that means "affection" or "love"; koi are therefore symbols of love and friendship in Japan.


Koi varieties are distinguished by coloration, patterning, and scalation. Some of the major colors are white, black, red, yellow, blue, and cream. While the possible colors are virtually limitless, breeders have identified and named a number of specific categories. The most notable category is Gosanke, which is made up of the Kohaku, Taisho Sanshoku, and Showa Sanshoku varieties.

New koi varieties are still being actively developed.[8] Ghost koi developed in the 1980s have become very popular in the United Kingdom; they are a hybrid of wild carp and Ogon koi, and are distinguished by their metallic scales. Butterfly koi (also known as longfin koi, or dragon carp), also developed in the 1980s, are notable for their long and flowing fins. They are hybrids of koi with Asian carp. Butterfly koi and ghost koi are considered by some to be not true nishikigoi.[citation needed]

The major named varieties include:

  1. Kohaku
  2. Taisho Sanke
  3. Showa Sanke
  4. Tanchō
  5. Chagoi
  6. Asagi
  7. Utsurimono
  8. Bekko
  9. Goshiki
  10. Shūsui
  11. Kinginrin
  12. Kawarimono
  13. Ōgon
  14. Kumonryū
  15. Ochiba
  16. Koromo
  17. Hikari-moyomono
  18. Kikokuryū
  19. Kin-Kikokuryū
  20. Ghost koi
  21. Butterfly koi
  22. Doitsu-goi

Differences from goldfish[edit]

Koi have prominent barbels on the lip that are not visible in goldfish.

Goldfish were developed in China more than a thousand years ago by selectively breeding Prussian carp for color mutations. By the Song Dynasty (960 – 1279), yellow, orange, white, and red-and-white colorations had been developed. Goldfish (Carassius auratus) and Prussian carp (Carassius gibelio) are now considered different species. Goldfish were introduced to Japan in the 16th century and to Europe in the 17th century.[2] Koi, on the other hand, were developed from common carp in Japan in the 1820s. Koi are domesticated common carp (Cyprinus carpio) that are selected or culled for color; they are not a different species but a subspecies, and will revert to the original coloration within a few generations if allowed to breed freely.

In general, goldfish tend to be smaller than koi, and have a greater variety of body shapes and fin and tail configurations. Koi varieties tend to have a common body shape, but have a greater variety of coloration and color patterns. They also have prominent barbels on the lip. Some goldfish varieties, such as the common goldfish, comet goldfish, and shubunkin have body shapes and coloration that are similar to koi, and can be difficult to tell apart from koi when immature. Since goldfish and koi were developed from different species of carp, even though they can interbreed, their offspring are sterile.[10]

Health, maintenance and longevity[edit]

Traditional Japanese garden with koi

The common carp is a hardy fish, and koi retain that durability. Koi are cold-water fish, but benefit from being kept in the 15-25 °C (59-77 °F) range, and do not react well to long, cold, winter temperatures; their immune systems are very weak below 10 °C. Koi ponds usually have a metre or more of depth in areas of the world that become warm during the summer, whereas in areas that have harsher winters, ponds generally have a minimum of 1.5 metres (4½ feet). Specific pond construction has been evolved by koi keepers intent on raising show-quality koi.

Koi's bright colours put them at a severe disadvantage against predators; a white-skinned Kohaku is a visual dinner bell against the dark green of a pond. Herons, kingfishers, otters, raccoons, cats, foxes, badgers and hedgehogs are all capable of emptying a pond of its fish. A well-designed outdoor pond will have areas too deep for herons to stand, overhangs high enough above the water that mammals cannot reach in, and shade trees overhead to block the view of aerial passers-by. It may prove necessary to string nets or wires above the surface. A pond usually includes a pump and filtration system to keep the water clear.

Koi are an omnivorous fish, and will eat a wide variety of foods, including peas, lettuce, and watermelon. Koi food is designed not only to be nutritionally balanced, but also to float so as to encourage them to come to the surface. When they are eating, it is possible to check koi for parasites and ulcers. Koi will recognize the persons feeding them and gather around them at feeding times. They can be trained to take food from one's hand. In the winter, their digestive systems slow nearly to a halt, and they eat very little, perhaps no more than nibbles of algae from the bottom. Feeding is not recommended when the water temperature drops below 10 °C (50 °F).[11][12] Care should be taken by hobbyists that proper oxygenation and off-gassing occurs over the winter months in small water ponds, so they do not perish. Their appetites will not come back until the water becomes warm in the spring.

There are reports of kois that have achieved ages of 100–200 years.[13] One famous scarlet koi, named "Hanako," was owned by several individuals, the last of whom was Dr. Komei Koshihara. In July 1974, a study of the growth rings of one of the koi's scales reported that Hanako was 225 years old.[14] The greatest authoritatively accepted age for the species is little more than 50 years.[15][16]


Koi are very hardy. With proper care, they resist many of the parasites that affect more sensitive tropical fish species, such as Trichodina, Epistylis, Ich and other ciliated protozoans. Two of the biggest health concerns among koi breeders are the koi herpes virus (KHV) and Rhabdovirus carpio, which causes spring viraemia of carp (SVC). No treatment exists for either disease. Some Koi farms in Israel use the KV3 vaccine, developed by Prof. M. Kotler from the Hebrew University and produced by Kovax, to immunise fish against KHV. They are currently the only country in the world to vaccinate koi carp against the Koi Herpes Virus. The vaccine is injected into the fish when they are under one year old, and is accentuated by using an ultraviolet light. The vaccine has a 90% success rate[17] and when immunised the fish cannot succumb to a KHV outbreak and neither can the immunised koi pass KHV onto other fish in a pond.[18] Only biosecurity measures such as prompt detection, isolation and disinfection of tanks and equipment can prevent the spread of the disease and limit the loss of fish stock. In 2002, spring viraemia struck an ornamental koi farm in Kernersville, North Carolina, and required complete depopulation of the ponds and a lengthy quarantine period. For a while after this, some koi farmers in neighbouring states stopped importing fish for fear of infecting their own stocks.

[19] [20]


Koi in an outdoor koi pond

Like most fish, koi reproduce through spawning in which a female lays a vast number of eggs and one or more males fertilize them. Nurturing the resulting offspring (referred to as "fry") is a tricky and tedious job, usually done only by professionals. Although a koi breeder may carefully select the parents they wish based on their desired characteristics, the resulting fry will nonetheless exhibit a wide range of color and quality.

Koi will produce thousands of offspring from a single spawning. However, unlike cattle, purebred dogs, or more relevantly, goldfish, the large majority of these offspring, even from the best champion-grade koi, will not be acceptable as nishikigoi (they have no interesting colors) or may even be genetically defective. These unacceptable offspring are culled at various stages of development based on the breeder's expert eye and closely guarded trade techniques. Culled fry are usually destroyed or used as feeder fish (mostly used for feeding arowana due to the belief it will enhance its color), while older culls, within their first year between 3" to 6" long (also called "Tosai"), are often sold as lower-grade, pond-quality koi.

The semirandomized result of the koi's reproductive process has both advantages and disadvantages for the breeder. While it requires diligent oversight to narrow down the favorable result the breeder wants, it also makes possible the development of new varieties of koi within relatively few generations.

In the wild[edit]

See also: Common carp

Koi have been accidentally or deliberately released into the wild in every continent except Antarctica. They quickly revert to the natural coloration of common carp within a few generations. In many areas, they are considered an invasive species and pests. They greatly increase the turbidity of the water because they are constantly stirring up the substrate. This makes waterways unattractive, reduces the abundance of aquatic plants, and can render the water unsuitable for swimming or drinking, even by livestock. In some countries, koi have caused so much damage to waterways that vast amounts of money and effort have been spent trying to eradicate them, largely unsuccessfully.[21] In many areas of North America, koi are introduced into the man made "water hazards" and ponds on golf courses in order to keep water born insect larvae under control through predation.[22] In Australia, they are noxious fish.[23]

See also[edit]


  1. ^ "Pictures available for Cyprinus carpio haematopterus.". www.fishbase.org. Retrieved 2010-10-31. 
  2. ^ a b "Background information about goldfish". Retrieved 2006-07-28. 
  3. ^ "History of common carp aquaculturing". Retrieved 2010-07-29. 
  4. ^ "MPKS Ray Jordan Koi History". Ray Jordan. Retrieved 2009-04-26. 
  5. ^ "Early Records". Netpets.org. Retrieved 2009-04-11. 
  6. ^ a b Grossa, Riho; Klaus Kohlmannb and Petra Kerstenb (February 2002). "PCR–RFLP analysis of the mitochondrial ND-3/4 and ND-5/6 gene polymorphisms in the European and East Asian subspecies of common carp (Cyprinus carpio L.)". Aquaculture (Elsevier) 204 (3–4): 507–516. doi:10.1016/S0044-8486(01)00836-5. 
  7. ^ "Discovery of an ancient lineage of Cyprinus carpio from Lake Biwa, central Japan, based on mtDNA sequence data, with reference to possible multiple origins of koi
  8. ^ "Guide to Koi Varieties". Retrieved 12 April 2014. 
  9. ^ Tamadachi M (1990). "Koi varieties". The Cult of the Koi. Neptune City, New Jersey: TFH Publications. p. 191. ISBN 0-86622-085-2. 
  10. ^ "Aquatic-oasis articles". Aquatic-oasis. Retrieved 2012-02-02. 
  11. ^ "Koi Feeding Guide". Retrieved 2 October 2013. 
  12. ^ "Temperatures to feed koi fish". Retrieved 1 April 2014. 
  13. ^ Felicity Huntingford; Malcolm Jobling; Sunil Kadri (13 February 2012). Aquaculture and Behavior. John Wiley & Sons. pp. 12–. ISBN 978-1-4051-3089-9. "... and there are reports of fish that have achieved ages of 100–200 years (Purdom 1993; Billard 1999)." 
  14. ^ Barton, Laura (2007-04-12). "The Guardian". London: The Guardian. Retrieved 2009-04-11. 
  15. ^ Carwardine, Mark (2008). Animal Records. Sterling Publishing Company. p. 201. ISBN 9781402756238. 
  16. ^ "AnAge entry for Cyprinus carpio". 
  17. ^ http://www.kovax.co.il/products/kv3-vaccine-against-khv/
  18. ^ http://www.mitchkoi.co.uk/media/In-Focus-KHV.pdf
  19. ^ http://www.sfbakc.org/Articles/SVC_Impact.htm
  20. ^ http://koisale.com/inprogress2/ourkoi.php
  21. ^ USGS Non-indigenous Aquatic Species Program
  22. ^ Terraforming America: Using Invasive Species For A Greater Good. by Daniel Teague. 1989.
  23. ^ Carp:Noxious fish


http://www.sfbakc.org/Articles/SVC_Impact.htm impacts of SVC Spring Viremia of Carp

External links and further reading[edit]

Media related to Koi at Wikimedia Commons